1. Field of Invention
This invention relates to a method for preparing ultrathin piezoelectric resonator plates, and particularly to a method for trimming the thickness of the vibrating portions of a plurality of ultrathin piezoelectric resonator plates formed in a wafer of a piezoelectric material without excessive or incomplete trimming.
2. Prior Art
As the demand for reduction in size or thickness or operation at higher frequencies of electronic instruments and apparatuses becomes severe, in addition to miniaturization of piezoelectric resonators used in oscillators or filters, raising of their resonance frequency and reduction of the temperature dependency of their resonance frequency are also required.
In view of this tendency, the inventor of this invention established a basic manufacturing process of an ultrathin piezoelectric resonator using AT-cut quartz crystals with a vibrating portion of about 15 .mu.m in thickness enclosed by a thicker peripheral portion which has a fundamental vibration frequency higher than 100 MHz.
In the manufacturing process of the ultrathin piezoelectric resonator, a plurality of depressions are formed in one side of a wafer of a piezoelectric material to form ultrathin vibrating portions as the bottom wall of each depression. The thickness of the vibrating portions thus formed does not fall within a desired range of variation from a predetermined value. Therefore, the thickness of each vibrating portion is measured to determine the thickness trim and trimmed by etching. Since the distance between adjacent depressions is very small and the depth of depressions is only approximately 60 to 70 .mu.m, there are the following problems with this trimming process: the etching liquid dropped in a depression can overflow into adjacent depressions; the vapor of the etching liquid corrodes the vibrating portions which do not need trimming and makes them too thin; and an insufficient dropping of the etching liquid can be caused by a slight fluctuation of the operation of the etching liquid dispenser and the sufficient amount of the etching liquid evaporates out before a determined etching time elapses to cause incomplete trimming.